osu/osu.Game.Rulesets.Mania/MathUtils/FastRandom.cs

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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
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using System;
namespace osu.Game.Rulesets.Mania.MathUtils
{
/// <summary>
/// A PRNG specified in http://heliosphan.org/fastrandom.html.
/// </summary>
internal class FastRandom
{
private const double int_to_real = 1.0 / (int.MaxValue + 1.0);
private const uint int_mask = 0x7FFFFFFF;
private const uint y = 842502087;
private const uint z = 3579807591;
private const uint w = 273326509;
internal uint X { get; private set; }
internal uint Y { get; private set; } = y;
internal uint Z { get; private set; } = z;
internal uint W { get; private set; } = w;
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public FastRandom(int seed)
{
X = (uint)seed;
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}
public FastRandom()
: this(Environment.TickCount)
{
}
/// <summary>
/// Generates a random unsigned integer within the range [<see cref="uint.MinValue"/>, <see cref="uint.MaxValue"/>).
/// </summary>
/// <returns>The random value.</returns>
public uint NextUInt()
{
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uint t = X ^ (X << 11);
X = Y;
Y = Z;
Z = W;
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return W = W ^ (W >> 19) ^ t ^ (t >> 8);
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}
/// <summary>
/// Generates a random integer value within the range [0, <see cref="int.MaxValue"/>).
/// </summary>
/// <returns>The random value.</returns>
public int Next() => (int)(int_mask & NextUInt());
/// <summary>
/// Generates a random integer value within the range [0, <paramref name="upperBound"/>).
/// </summary>
/// <param name="upperBound">The upper bound.</param>
/// <returns>The random value.</returns>
public int Next(int upperBound) => (int)(NextDouble() * upperBound);
/// <summary>
/// Generates a random integer value within the range [<paramref name="lowerBound"/>, <paramref name="upperBound"/>).
/// </summary>
/// <param name="lowerBound">The lower bound of the range.</param>
/// <param name="upperBound">The upper bound of the range.</param>
/// <returns>The random value.</returns>
public int Next(int lowerBound, int upperBound) => (int)(lowerBound + NextDouble() * (upperBound - lowerBound));
/// <summary>
/// Generates a random double value within the range [0, 1).
/// </summary>
/// <returns>The random value.</returns>
public double NextDouble() => int_to_real * Next();
private uint bitBuffer;
private int bitIndex = 32;
/// <summary>
/// Generates a reandom boolean value. Cached such that a random value is only generated once in every 32 calls.
/// </summary>
/// <returns>The random value.</returns>
public bool NextBool()
{
if (bitIndex == 32)
{
bitBuffer = NextUInt();
bitIndex = 1;
return (bitBuffer & 1) == 1;
}
bitIndex++;
return ((bitBuffer >>= 1) & 1) == 1;
}
}
}